Please notice that some of the reasons presented here are general enough to be applied to any programming language (especially the bad reasons to learn a language). Others are specific of Java (especially the reasons to learn it).
Also keep in mind that the good reasons to learn Java will be presented in another post because this one is becoming far to long to be readable in the few minutes I feel entitled to ask you, dear reader. So believe me... you probably should learn Java. Still, not for the reasons I list here.
Not so good reasons to learn Java
It is widespread
You may be lead to think that since Java is a very widespread language, it is easier to find jobs if you know it. In the case of Java there is the question that I am convinced that it is not a bad thing to know Java and that can have pleasant effect on finding jobs (more on that later), still I would not consider it a good reason to learn Java.
Learning a widespread language means more jobs and more applicants. What really matters is the ratio between jobs demand and offer. And usually for very widespread languages it is not always very high. Skilled, experienced and "famous" developers do not care much. The others should.
It is object oriented
This and the variant "it is more object oriented" are clearly wrong reasons. There is plenty of good object oriented languages. And it is rather hard to decide which is more object oriented (lacking function looks more like a wrong design decision than a clue of being more object oriented).
Besides, I'm not even sure that being more object oriented is good (or bad for what matters). Well... not sure that being object oriented is inherently good either. Maybe in ten years the dominant paradigm will be another. Maybe in two. Three years ago "functional programming" was murmured in closed circles and outsiders trembled in fear at its very sound.
No, joking. Most people thought that "functional" meant having functions (and possibly no objects) and thought about C or Pascal. They did not know it was about not having crappy functions. Yeah, more than that, of course, but that's a start.
It is a good functional language
Just checking if you were reading carefully...
That is a bad reason because it is not true!
It is fast/slow
Oh, come on! Java implementations are decently fast, faster than most other language implementations out there and usually slower than implementations of languages such as C, C++, Fortran. Still, for some specific things it may be nearly as fast or faster. Sometimes it is not only CPU efficiency that matters.
It is good for concurrency
The "classic" Java threading model sucks. It's old. Nowadays other ways of doing concurrency are better (more efficient, easier to use).
Such more efficient easier to use methods are built-in in languages such as Clojure (or Scala, or Erlang). Still, Java is probably the most supported platform in the world. Such concurrency models are not inside the language, but you may have them using libraries.
Sometimes this is a real PITA (language support is a great thing, because the syntax is closer to the semantics).
Moreover having the "older" concurrency model visible may be a problem with the newer stuff. And some other libraries and frameworks may just assume you want to do things the old way.
It is good for the web
Ok... most people do not even know how widespread is Java on the web. In fact, it is. But is it really good? I do not really think so. There is lots of good stuff in Java world for the web, of course. The point is that there is also for other platforms. Here Rails and Django spring to mind.
Moreover, there is loads of extremely cool stuff coming from the functional world. Erlang and Haskell have some terrific platforms. Scala and Clojure also have some extremely interesting stuff and can leverage mature Java stuff but make it really easier to use.
Grails (web framwork) may seem on the same wavelength, still I think there is a very important difference. First, I don't like Groovy at all. In fact Groovy very author says that he would not have created it if he knew Scala. And of course since I do not like Groovy, I do not see why I should be using Grails, which, as far as I know, does not offer killer features over Rails or Django.
Scala and Clojure are different. They are not just "easier" than Java. They teach a different way of thinking and approaching development. And of couse, they are great for the web also.
I already know it a bit
This is quite an interesting point. Why, if you know a language a little, shouldn't you learn it well? This essentially makes it clear the difference between a not so good reason to learn something and a reason not to learn it.
The point is simple: if you are interested in learning Java (for the good reasons), do it. But from knowing a language "a bit" and knowing it "well" there is quite the same distance that from not knowing it and knowing it well. So don't do it because you think your prior experience may be extremely relevant.
There are languages which are just easier to master (where easier means that to learn them from scratch it takes less time that to become as proficient in Java as you would learning those languages -- yeah, Python, Ruby, ...)
Besides, I feel that the second step in Java is rather hard. I think that Java is very easy to learn for experienced developers (it is not a joke). The very first step in Java is relatively easy (a part from lots of useless crap like having to declare a class to put there a static main method and overly complicated streams). The step just after that, the one that takes you from writing elementary useless programs to writing elementary useful programs is quite harder, since lots of useful stuff in Java requires to understand OO principles quite well to be used without too many surprises.
So, you may have learnt Java at the college. Still, if you to hack something and "grow" there are languages that let you do it faster (Python or Ruby).
I have to
This is the worse possible reason because I don't see the spark in it. You have to. You probably are an experienced developers that got bored to death reading this post, you did not know Java and you have to learn it. Maybe your boss wants you to do some Java.
I'm sorry for you. Java is not easy to learn (especially to learn it at the point you can work with it). Mostly because everybody has been doing Java in the last fifteen years. Smart people and dumb people.
As a consequence there are truly spectacular pieces of software it is a pleasure to work with and worthless pieces of over-engineered crap. I truly hope that you are going to work with the great stuff.
Still I consider a "bad reason" to learn a language, because you are probably not going to enjoy the learning process. If you were, you would have used a different sentece... like "I want to".
And perhaps the thing would have been "My boss gives me the opportunity to increase my professional assets learning this new technology, Java".
It was easier to download/find a book/my cousin knows it.
One of the most popular reasons people pick up a language is because they find it installed on their system. That is not usually the case for Java, in the sense that usually the JDK is not installed, even if the VM is. Variants of this argument are a friend proficient in the language or, more frequently, availability of books at the local bookstores. This kind of arguments usually apply for complete programming beginners or people who had prior experience that has not been refreshed for years (e.g., old Basic programmers).
It is true that it is easy to find manuals for Java. The point is that not every manual is a good starting point. Specifically, this kind of user really needs a manual targeted at a true beginner. Unfortunately, that is the category of books where more craps piles. First beginners usually do not really understand if the manual they are using is crap.
If their learning process is too slow (supposed that they see it) they usually blame: (i) programming in general, (ii) the language or, worse (iii) themselves. Well, the language may have its faults (especially in the case of Java, still C++ is worse for a beginner), but it is important to understand that the culprit is usually the manual.
The funny thing is that the people who know how to tell apart a good manual from a bad one are usually the ones that do not really need an introductory book, are probably not going to buy it and more often than not are not enquired about a good manual. So unless their cousin is actually a skilled programmer, beginners are really risking buying a bad manual. And please, notice that even skilled programmers are susceptible to a similar argument: if you are interested in a new language and you read a terrible manual you may build a wrong opinion on the language (and perhaps you are not interested in spending another 40 gold coins to convince you that the language is really bad).
So please: read reviews on Amazon (or similar site -- notice that I'm not going to suggest to buy from Amazon, even if I often do and I am an associate -- here I'm just saying that the amount of reviews on books on Amazon -- com -- is usually large enough to make an idea). Find people that are experts and have teaching experience: their reviews are probably the one to base the judgment upon. Then buy the book from whatever source you want.
So do not buy a Java book because you can find books on Java and not on Clojure/Python/Ruby/Whatever. Choose the language (this is hard), choose the book (this is easier), buy, read it, study it, code code code.
- I kind of found out that for people really convinced that learning a language is easy one or more of the following apply:
- have an unmotivatedly high opinion of their knowledge of the languages they claim to have learned
- have a very inclusive definition of "learning" a language (e.g., writing hello world in it)
- only know and learn very similar languages (really, if you know C++ it's gonna be relatively easy to pick up Java, if you know Scheme probably Clojure is not going to be a big deal, etc.)
- and tend to write "blurb" in every language they know (so for example they write Python as if it was C++ -- and usually are very surprised when things go badly)
- It is funny that I am suggesting to learn only "object oriented dynamic" languages such as Python or Ruby. I understand that many advocates of functional programming may disagree. But I somewhat think that while some kind of people greatly benefit from learning a functional language as the first language they truly master, many others are just not fit for functional programming because it is too abstract and working imperatively may be easier for them. As a consequence, languages such as Python or Ruby may naturally lead you towards functional programming if it is the kind of stuff you like, but are still usable if you are not that kind of person. I have seen things...
And yes... if you are the kind of person that likes functional programming, you will get into functional programming sooner or later. This is just a bit later.
- Notice Clojure here...
- Whatever is not a language. Still, it would be a great name for a language. Maybe not.